Approximately half of the world's population relies upon biomass fuels – such as wood, dung and agricultural wastes – for everyday tasks such as cooking, drying crops and purifying water. Although biomass fuel has the potential to be virtually carbon neutral, the demand for cooking wood is driving deforestation in some parts of the world.

In addition, if the biomass is burned in an open fire or a typical inefficient stove, the combustion produces not only CO2 but relatively large quantities of soot, as well as powerful greenhouse gases such as methane, carbon monoxide and nitrous oxide.

Simple but super-efficient "rocket" stoves, of the type advocated in Manchester by Peter Scott, help tackle all of these problems. They reduce the amount of wood required, taking pressure off forests. They slash emissions of soot and greenhouse gases, reducing the climate change impact by more than 50%, and they reduce local air pollution, which helps limit the incidence of lung and eye disease. As a bonus, efficient stoves can significantly reduce the time that families need to spend gathering wood.

A simple but efficient "rocket" stove can be produced for as little as £4 ($7) and can save the equivalent of 1–3 tonnes of CO2 per year. This makes it one of the least expensive ways to tackle global warming, even before you consider the social benefits.